The primary hypothesis to be tested in this project is that by 6 months of age infants respond to an interpersonal stress with specific coping strategies and specific emotional reactions. However, because a multiplicity of factors modify the infant's strategies, the following secondary hypotheses will also be examined: 1) that these specific reactions are affected by the infant's previous interpersonal history; 2) that they are affected by the infant's temperament; and 3) that 6 month olds exhibit stable individual differences in these reactions. To test these hypotheses, forty male and forty female 6 month old infants and their mothers will be subjects. At two sessions, separated by a week, they will experience a normal interaction followed by a stressful interaction followed by another normal interaction. The stressful interaction will be the mother acting still faced and unresponsive. The sessions will be videotaped. The infant's behavior will be scored from the tapes for coping strategies using Gianino's Self-Regulatory Scoring System (Gianino, 1982) and for affective displays using Izard's AFFEX system (Izard & Dougherty, 1982). The mother's behavior will be scored from the tapes for sensitivity using Ricks' Maternal Sensitivity and Responsivity Scales (Ricks, 1981). And infant tempeament will be assessed with Rothbart's Infant Behavior Questionnaire (Rothbart, 1981). Data will be analyzed using correlational techniques, analyses of variance, and lag sequential techniques to define differences between infant reactions to the normal and stressed interaction and to examine the relationship of those reactions to maternal sensitivity and temperament and to test their stability over time.